Plot hole: The movie is based in 1986 after the group time travels from 2010. That makes it a 24 year trip back in time. It is stated that Jacob is 20 years old. That is an error as this would make him roughly around 23 or 24 if he was conceived in 1986, which we saw near the end of the movie.
Suggested correction: This mistake has already been corrected. Cusack could have simply generalized his age when he mentioned it, probably not remembering his real age at the moment.
Plot hole: When Gawain is repairing the hole in the vault wall, a security camera is visible in the top corner in the room.
Plot hole: Cindy manages to pick Crisp out of a line-up even though she was hidden in a box and didn't see him, she only heard his voice. But even with that, he isn't asked to speak during the line-up.
Plot hole: In the opening of the film, some of the characters are flipping through a scrapbook they've made documenting Elle's experiences in the first film. The problem is that many of the pictures are of moments when no photos were taken, so how did they get the pictures to put in the scrapbook?
Plot hole: When the students are breaking into ETS, they take great care to avoid the security cameras in the lobby; donning masks, crawling on the ground, etc. Yet a bit later, two of them go back to guard the same lobby, they are seen walking around and sitting on the desk that they so carefully crawled past earlier.
Plot hole: The Hillbillies take a "short cut" to catch up with the guys after they are taken in by Burt Reynolds. However, the guys get a chance to sleep comfortably until morning before being confronted by them. (01:12:10)
Plot hole: It takes less than 3 minutes to fill the house with water using a mere garden hose? I mean come on...
Plot hole: Michael McKean quits pursuing Beldar and approximately 15 years pass as indicated by Connie growing up, yet when you see McKean again and his assistant, they have not aged at all.
Plot hole: While planting the suicide gear in the bathroom before Buckley comes in, Cooper tells Josh to tie the rope into a noose as they go to hide in the shower. Josh replies that he doesn't even know how to tie a noose. He must be a quick study, because in the 45 seconds or so that it would have taken Buckley to relieve himself and wash his hands, Josh has tied a perfect noose. (01:03:55)
Plot hole: The policeman survives a frontal crash into the hillbilly's truck at full speed without as much a scratch. (00:24:40)
Plot hole: Edward Lionheart severs the head of theater critic Horace Sprout while Sprout and his wife are asleep. (Lionheart gave them both a knockout injection). Sprout's wife (and his maid)discover the severed head in the morning, and both scream and faint. But in the next scene, critic Perry Devlin retrieves his morning newspaper and then reaches for his bottle of milk, only to find Sprout's head perched on the milk bottle. How did the head get from Sprout's house to Devlin's place?
Plot hole: The fact that David becomes conscious after being hit and left back is dramatically fine but there is no aftermath - he misses to finish dealing with Ali and friends at that point.
Plot hole: When Hugh is walking near the park gate, he should have seen Marcus. Marcus was on the same side of the post as Will was.
Plot hole: At the end of the film the boss says that he and Miss Fitzgerald are going to go on holiday together to Paris (talking about the actual city, not the secret code they have invented). However, the film is set in 1940 and Paris would have been an unusual place to take a holiday at this time, considering France was in the middle of a war... Pretty dangerous for civilians even though America was still neutral at the time.
Plot hole: The sheer distances Kevin covers on foot in one night are outrageous. Between 9pm and midnight he walks from Carnegie Hall to the children's hospital, to 95th street, back to the toy store carrying a large paint can and a large 2x4 (street signs here put it around 59th and 5th), back up to 95th, then all the way back to midtown, to Rockefeller Plaza. One way from W 95th street to around E 59th and 5th Ave. is at least an hour on foot for an adult, he does this 4 times between 9pm and midnight, once while carrying a 2x4 and paint can, once while being chased by 2 adults, and he still has time to set up a house full of traps.